British vs American English – Why Is “Math” Pluralized in British English But Singular in American English?

One thing to keep in mind is that for a long time, people lived "in" Cavendish. Note that there may have been a couple roads in Cavendish, none of which had names, but you were speaking of a geographical entity rather than a linear place. Even as recently as 1998, when I lived in Kathmandu, you could be in "Thamel" or Jawalakel (two neighborhoods), but on any one of about 6 streets.

Americans, having lived less long in ancient place areas view roads more as routes rather than locales, hence the differentiation - Americans live on a route between two places, whereas Britons live in a place, that has taken on a road name.

As a native speaker of Midwestern American English, I don't hear my accent as an "accent", naturally, but I know it's there. Any English speaker will recognize that I'm American as soon as I open my mouth and start talking English (I occasionally do better in other languages), and they'll probably recognize my accent as "Midwestern", if they've ever heard of it.

So it's not true that Midwesterners don't have accents; we do. As Schrödinger's Cat points out, everyone has an accent.

Possibly -- and here's the germ of truth in this myth -- it may be the fact that Midwestern English is the standard dialect for national broadcasting in the United States that people are referring to. Just as RP is standard on the BBC (with special exceptions for Northern dialects), Midwestern is standard in the US (with exceptions, mostly for Southern dialects).

That's all.

Don't believe everything you hear about English. In fact, generally it's a good idea not to believe anything you hear about English; there's an awful lot of nonsense around.